Parapet walls enclose and support the deck frame, while a watertight rubber roof protects the living space below

In the coastal area where I design and build homes, it's often
important to make the most of the views, light, and breezes
that a shoreline site offers. Many times, I find that a high
deck is the best way to reveal a beautiful ocean view, or
perhaps just to catch a glimpse of the water over dunes or
neighboring buildings.

Working primarily in the Shingle Style, which typically
involves a lot of dormered spaces under roofs, I often end up
setting those decks into the roofline above a lower-story room.
It's also convenient in many cases to build a deck on top of
one of the many-sided projecting rooms I like to use for
catching light, views, and oceanside breezes. In house after
house, I've found that a deck sitting on a roof provides a lot
of value for the owner. It makes sense to me, in light of my
own experience, that the "widow's walk" has been such a popular
element on homes in this area through the years.

When I started to use rooftop decks more than 12 years ago, I
looked around at some examples built by others. EPDM rubber
membranes make an excellent low-slope roof covering, and it's
not hard to build a deck sitting on sleepers that rest on the
membrane itself; but I've never liked that method. For one
thing, the sleepers tend to compress the foam-board
underlayment used for those EPDM systems, creating a slight
trough or depression in the roof surface. And they tend to dam
up the water that should flow freely off the roof. Debris and
grime quickly start to collect in the low spots around the
sleepers and, after a few years, accumulate on the roof just
below the walking surface.

To avoid those problems, I worked out a design that suspends
the deck frame an inch or two above the rubber roof, supported
by parapet half-walls that rise above the roof plane as a
continuation of exterior or interior house walls (see Figure
1). That way, the deck structure never contacts the roof
surface at all — instead, a continuous drainage space
lets water (and dirt) flow freely off.

The author's design for rooftop decks
protects the structure and living space of the room below with
a continuous EPDM roof. To allow free drainage and protect the
roofing, the deck frame is suspended from the parapet
walls.

On the other hand, the deck still shades the watertight EPDM
surface and protects it from damaging sunlight. That extends
the service life of the rubber (which is good for 30 years or
more, even when it isn't shaded). I've built at least 25
roof-and-deck combinations using this design over the last
dozen or so years, all exposed to harsh seaside conditions that
can eat the enamel off a doorknob in about three months
— and I haven't had a single callback.

For an example of how it's done, I'll use the deck we
installed over a bumpout room on the same Rhode Island custom
home that I described in
"Shearwalls for
Coastal Homes" (2/04). On that house, a projecting octagon
room facing the ocean served the design in several ways: It
efficiently opened up interior space; it provided nice views,
light, and air; and it also helped to stiffen the house frame
against coastal windstorm forces. With parapet walls, a rubber
roof, and a deck assembly placed above it, the room serves yet
another function: It supports a protected but open upper-story
deck, graced with a nice view and plenty of sunshine.

Roof Framing

The room's roof framing, which is also the ceiling framing for
the room below, really resembles a floor frame more than the
usual roof frame (Figure 2).

Figure 2.The ceiling joists of the room below the
deck are ripped to provide a slight pitch away from the house,
then sheathed with 1/2-inch plywood (left). Strapping helps
ensure a flat drywall ceiling (right).

The house walls do the work of supporting the above-roof
walking deck, and the deck framing itself is sized to carry the
design dead and live loads for our area, including snow loads.
So although it is capable of considerably more, the
roof-ceiling frame for the room isn't actually subjected to
loading much beyond its own weight. Depending on the dimensions
of the space, I'll use 2x8s or 2x10s for joists, with 1x4
strapping on the underside and 1/2-inch plywood sheathing on
the upper side. We rip the tops of the joists to provide a
pitch of about an inch, creating a gentle slope away from the
house.